Secrets of sperm-storing female snakes revealed

A snake curator studying in Darwin may have solved a puzzle that has confused experts for years.

Just how can some female snakes store sperm after mating, sometimes for months, before using it to fertilise their eggs?

The rare phenomenon has been recorded in snakes in different parts of the world.

Now Luke Allen, who curates a venom laboratory in South Australia, has used his captive snakes to find out how.

Storing sperm for six months

Studying the coastal taipan, Australia's longest venomous snake and one of the deadliest snakes in the world, he learned that the snakes can store sperm for up to six months after mating.

To do so he believes they use special cells in their bodies that secrete sugars and proteins to keep the sperm alive.

The sperm are kept in small pockets along a spongy tube that leads to the snakes' ovaries.

"It had been known that they had this ability but we didn't know how or why," said Mr Allen, who studies Environmental Science at Charles Darwin University.

Survival advantage

His six-year study also hinted at why snakes store sperm for such long periods.

The answer is bad news for people who dislike the creatures, which live in northern Australia and parts of Papua New Guinea.

"We found it was related to the food available," he said.

By altering the number of rats he gave them to eat, Mr Allen learned that when conditions were good the snakes could give birth to three clutches of eggs after a single mating.

Storing the sperm from a single coupling meant they could produce three times as many eggs than would have been possible if they did not have the ability.

If times were tough and the snakes were not fed as much they used the sperm all at once.

How sperm-storing snakes came to exist

Mr Allen said while conditions for coastal taipans were fairly stable, the snake was a close relative of the inland taipan, which sometimes had to go for years between rainy periods in Central Australia.

It is this variability which may have given rise to the unusual ability.

But the coastal taipan is not the only snake in the world to be able to delay the fertilisation of its offspring.

A rattlesnake in the USA kept alone in captivity for five years unexpectedly gave birth in 2010 to 19 snakelets, according to a report.

Other snakes can have so-called "virgin births" where they give birth to healthy young without the need to mate.